Ferrule with plural inner diameters

ABSTRACT

High localized loading, galling, and high torque forces have been generally eliminated or greatly reduced in a two ferrule tube fitting assembly through suitable modification of the rear ferrule so as to redirect the reaction forces acting between the front ferrule and the drive nut. The rear ferrule has a cylindrical interior wall that closely surrounds the tube end and is provided on the interior cylindrical wall with a circumferentially continuous radial recess that is located between the nose and rear wall of the rear ferrule. The rear ferrule also has a radially external wall that is substantially conical and additionally shaped to extend radially outward toward the enlarged diameter portion or flange of the rear ferrule. The rear ferrule further includes a contoured face on the rear driven surface of the ferrule that engages the drive surface of the drive nut.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/374,026, filed on Feb. 25, 2003 for FERRULE WITH RELIEF TO REDUCEGALLING, which is a continuation of U.S. patent application Ser. No.09/469,549 filed on Dec. 12, 1999 for FERRULE WITH RELIEF TO REDUCEGALLING, now U.S. Pat. No. 6,629,708, which is a continuation-in-part ofU.S. patent application Ser. No. 09/054,186 filed on Apr. 2, 1998, nowU.S. Pat. No. 6,131,963, which is a continuation-in-part of U.S. patentapplication Ser. No. 08/834,255 filed on Apr. 15, 1997, now U.S. Pat.No. 5,882,050, the entire disclosures of which are fully incorporatedherein by reference.

BACKGROUND OF INVENTION

The subject invention is directed to the art of ferrule type tubefittings. More particularly, the invention concerns a two ferrulefitting wherein the rear ferrule is designed to reduce the torquerequired to rotate the associated nut and to also reduce galling betweenthe rear ferrule and the interior surface of the drive nut. Theinvention may also be applied in a single ferrule fitting.

A commercially available and highly successful two ferrule fitting usedfor tubing is illustrated in FIGS. 1 and 1A. FIG. 1 shows the fittingcomponents in a finger tight position preparatory to final tightening,whereas FIG. 1A shows the fitting after final tightening. As shown, thefitting comprises a body 10 having a cylindrical opening 12 counterboredfor receiving tube end 13. A tapered, frusto-conical camming mouth 14 islocated at the axial outer end of the counterbore. A front ferrule 16having a smooth, cylindrical inner wall 18 is closely received on thetube. The front ferrule has a frusto-conical outer surface 20 to bereceived in the camming mouth.

Associated with the front ferrule 16 and located axially outwardtherefrom is a rear ferrule 22 configured as shown with a tapered noseportion 24 and a rear flange 26 having an inclined end surface 28. Theinclined end surface of the rear ferrule 22 provides a radial componentas well as an axial component of the pull-up forces acting on the endsurface as will be apparent to those skilled in the art. The taperednose 24 enters a tapered camming surface in the rear surface of thefront ferrule.

The ferrules 16, 22 are enclosed by a drive nut member 30 threaded tothe body 10. During tightening and make-up of the fitting, the inner endface, flange, or shoulder 32 of the nut acts against the inclined endsurface 28 of the rear ferrule to drive the ferrules forwardly into thefully engaged position shown in FIG. 1A.

The small diameter portion or nose of the rear ferrule is dimensioned sothat it plastically deforms during make-up of the fitting. This actionis desirable since it results in tight gripping engagement of the outerwall of the tubing. The thickness of the nose portion cannot be reducedto an extent that the rear ferrule deforms too much and only the rearferrule adequately grips the outer wall of the tubing. That is, the twoferrule assembly requires desired deformation of both the front and rearferrules for the gripping and sealing capabilities that have made thistwo ferrule assembly a commercially successful product. On the otherhand, the thickness of the nose of the rear ferrule cannot be enlargedto such an extent that it results in a structural arrangement that istoo stiff and does not permit the desired rear ferrule deformation.

A more complete description and understanding of the conventional twoferrule phase controlled sequential gripping action resulting from theinclined rear surface and the interaction of the front and rear ferrulesis set forth in U.S. Pat. No. 3,103,373 issued to Lennon, et al., theentire disclosure of which is fully incorporated herein by reference.

Accordingly, it will be recognized by those skilled in the art that apredetermined wall thickness of the nose of the rear ferrule is desiredthat achieves the desired gripping of the tube and cooperates with thefront ferrule in such a manner that it achieves its desired goals ofgripping and sealing the tube.

It is also recognized that operators of fluid systems test the systemprior to a production run by pressurizing the system to an appropriatefactor times the rated system pressure. In this manner, the operator caneasily detect whether the fluid system is sealed, i.e. that there are noleaks. With this knowledge, the manufacturer can provide a fitting inwhich the nose of the rear ferrule will not have any additional plasticdeformation at the elevated test pressure. Accordingly, the elevatedtest pressure is used to determine the desired wall thickness of thenose portion of the rear ferrule to achieve the desired amount ofdeformation of the nose and permit the front and rear ferrules toproperly grip and seal with the outer wall of the tube.

It has also been found that galling of the drive nut sometimes occurs inthe drive face area of engagement between the inner end face of thedrive nut and the rear wall of the rear ferrule. After analysis, it isbelieved that the axial thrust or pull-up force between the front andrear ferrule is essentially parallel to the axis of the fitting. Thisaxial thrust causes the rear corner region of the rear ferrule toselectively concentrate pull-up stress at the inside drive surface ofthe nut particularly in a localized area to produce the galling. Thisalso noticeably increases the nut torque forces experienced duringmake-up even if galling is absent. Accordingly, it would be highlydesirable to provide a design wherein the thrust forces do not producethe high localized loading with the resultant galling and high torqueforces.

SUMMARY OF INVENTION

In accordance with one embodiment of the invention, a tube fittingincludes a fitting body having a cylindrical bore for receiving a tubeend and including a tapered mouth at one end of the bore; a drive memberhaving a threaded engagement with the body and having a ferrule drivesurface; a first ferrule having a tapered first end that extends intothe tapered mouth of the fitting body and having a second end with atapered recess that axially extends toward the first end; and a secondferrule having a cylindrical interior wall, a tapered first end thatextends into the tapered recess of the first ferrule, and having acontoured face on a second end thereof that engages the drive memberferrule drive surface; the second ferrule interior wall having acircumferential recess located between the first and second ends of thesecond ferrule; the recess and the contoured face reducing stressconcentrations on the drive member drive surface when the fitting ismade up.

Another aspect of the invention includes forming the rear ferrule with acylindrical interior wall that has a first diameter at the forward ornose end of the ferrule and a second diameter at the rear end of theferrule wherein the second diameter is greater than the first diameterso that, for example, a single tool can be use to form thecircumferential recess and the cylindrical wall. Still a further aspectof the invention includes forming a notch on the outside diameter of theferrule body that joins the second ferrule first and second ends. Inanother aspect of the invention, a contoured drive surface is providedon the drive member rather than on the rear ferrule second end. Thepresent invention may also be practiced with ferrules that are made ofharder base metal than prior ferrules. The invention may also bepracticed with ferrules that have been case hardened either entirely orselectively on the ferrule surface. In general, the present inventionmay be used in single ferrule fittings as well.

These and other aspects and advantages of the present invention will beapparent to those skilled in the art from the following description ofthe preferred embodiments in view of the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The invention may take physical form in certain parts and arrangementsof parts, preferred embodiments and a method of which will be describedin detail in this specification and illustrated in the accompanyingdrawings which form a part hereof, and wherein:

FIG. 1 is a longitudinal cross-sectional view of a well known prior arttwo ferrule swage-type fitting;

FIG. 1A is an enlarged view of the circled area of FIG. 1 showing theprior art fitting in a made condition;

FIG. 2 is a view like FIG. 1 but showing a preferred embodiment of afitting incorporating a modified rear ferrule designed to improvereaction force transmission through the rear ferrule;

FIG. 3 is a greatly enlarged showing of the circled area of FIG. 2;

FIG. 4 is a detailed, partial cross-sectional view of a preferred formof rear ferrule;

FIG. 5 is a cross-sectional view similar to FIG. 4 showing a secondpreferred form for the rear ferrule;

FIG. 6 is a cross-sectional view of the fitting of FIG. 1 particularlyshowing the rear ferrule positioned between the front ferrule and thenut at initial make-up (graphically meshed for finite element analysis);

FIG. 7 is a view of the fitting of FIG. 6 in a made-up condition andillustrating the stress concentrations;

FIG. 8 is a cross-sectional view of a fitting at initial make-upincluding a rear ferrule modified in accordance with the teachings ofthe invention (graphically meshed for finite element analysis);

FIG. 9 is a view of the fitting of FIG. 8 in a made-up condition andillustrating the stress concentrations;

FIG. 10 is a cross-sectional view of a fitting at initial make-upincluding a rear ferrule modified in accordance with the teachings ofthe invention (graphically meshed for finite element analysis);

FIG. 11 is a view of the fitting of FIG. 10 in a made-up condition andillustrating the stress concentrations;

FIG. 12 is a cross-sectional view of a fitting at initial make-upincluding a rear ferrule modified in accordance with the teachings ofthe invention (graphically meshed for finite element analysis);

FIG. 13 is a view of the fitting of FIG. 12 in a made-up condition andillustrating the stress concentrations;

FIG. 14 is a table of different geometrical variations of the rearferrule configuration;

FIG. 15 is a cross-sectional view of an alternative embodiment of a twoferrule fitting;

FIG. 16 is an enlarged view of the ferrule region of the embodiment ofFIG. 15;

FIG. 17 is a partial view of a rear ferrule with a contoured face inaccordance with one aspect of the invention;

FIG. 18 is a partial view of a contoured rear ferrule shown in theengaged position with a front ferrule and drive nut surfaces prior topull up;

FIG. 19 is a view of the embodiment of FIG. 18 in the pulled upcondition showing stress distributions;

FIG. 20 is another embodiment of the invention;

FIG. 21 illustrates stress distributions in a two ferrule fitting thatdoes not use a contoured rear ferrule;

FIG. 22 illustrates another embodiment of a rear ferrule designincorporating a circumferential recess;

FIGS. 23A–F illustrate various alternative rear ferrule driven surfaceprofiles;

FIGS. 24A–G illustrates an alternative embodiment of the inventionwherein the drive surface of the nut is provided with a contour surface;

FIG. 25 illustrates another alternative embodiment of a ferrule havingan inner cylindrical bore formed of two different diameters;

FIG. 26 illustrates another alternative embodiment of a ferrule havingan outer notch or recess in the ferrule body;

FIG. 27 illustrates another alternative embodiment of the invention of aferrule having a notched inner bore, a contoured rear surface, an outernotch and a crown portion on the ferrule nose region; and

FIG. 28 is a finite element analysis illustrating one aspect of theinvention of a high friction tube grip area axially spaced from a stressriser created at the nose of the ferrule.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for the purposesof illustrating preferred embodiments of the invention only and not forpurposes of limiting same, FIG. 2 illustrate the overall arrangement ofa fitting incorporating the invention. It should be noted that in manyof the illustrations herein of the ferrule profiles, the ferrules areshown in partial cross-section for clarity and ease of understanding,particularly for views of the ferrule geometry and profile wherein it isonly necessary to illustrate a portion of the entire ferrule insectional view. The FIG. 2 embodiment has the major componentsidentified with the same reference numerals used with respect to thedescription of the prior art device of FIGS. 1 and 1A. A description ofa FIG. 1 element is to be taken as equally applicable to the FIG. 2elements that are correspondingly numbered unless otherwise noted. Inparticular, in the FIG. 2 embodiment, the rear ferrule 22′ has beenmodified in a manner to cause the reaction forces acting between thefront ferrule through the rear ferrule to the nut to have a significantforce component that is directed radially outward. This is incontradistinction to the FIGS. 1 and 1A embodiment wherein the forcecomponent under consideration has a high axial component. Specifically,as shown in FIG. 4, force component A extends generally axially of therear ferrule 22′ and results in an increase in the loads applied at theradial inner face of the rear ferrule driven surface 28′ and nutshoulder 32′. As previously discussed, high localized loading or stressconcentration in this area produces high torque and galling.

While the invention is described herein with particular reference to atwo ferrule system, such explanation is exemplary in nature and shouldnot be construed in a limiting sense. Various aspects of the presentinvention may also find application in a single ferrule fitting.

In one embodiment of the invention, a redirection of the reaction forcesis achieved by providing a circumferential recess 40 throughout theinner surface of rear ferrule 22′. Note that circumferential recess 40is located generally midway between the opposite ends of rear ferrule22′ and this results in the inner surface of the rear ferrule beingreduced to two relatively axially narrow substantially cylindrical andcontinuous contact areas 42 and 44. By so modifying the rear ferrule,the forces which are conducted from the front ferrule through the rearferrule to the nut shoulder 32′ tend to be directed more radiallyoutward such as diagrammatically illustrated by the force line B of FIG.4.

In this embodiment, the generally flat contact areas 42 and 44 havesubstantially the same diameter; however in an alternative embodiment,these two regions may have different diameters, for example it may bedesirable in some applications to have the diameter of the rear flatcontact area 42 slightly greater than the diameter of the forward flatcontact area 44, for example, by a few thousandths, more preferably oneto three thousandths of an inch. In yet a further alternativeembodiment, the rear flat contact area 42 may be eliminated as a contactarea by providing a counterbore in this area. Particularly for largerferrule sizes, the single flat in the nose section of the rear ferrulemay be sufficient to maintain proper ferrule alignment on the tubingduring installation. These alternatives will be more fully describedhereinafter.

Another important feature of the invention is best exemplified bycomparing the rear ferrule 22 of FIG. 1 with the rear ferrule 22″ of theFIG. 2 embodiment. Particularly, the outer radial wall 50 of the rearferrule 22″ includes a conical section that increases in radialdimension as it extends from the forward nose portion 52, that isreceived in the rear chamfer region 53 of the front ferrule, to the rearflange 26″. In the prior art arrangement (FIGS. 1 and 1A), the rearferrule has a cylindrical through bore and an outer radial wall thatextends parallel to the inner surface defining the through bore in thisregion. In other words, the rear ferrule has a constant annular wallthickness t. In the embodiment of FIG. 2 the outer wall has the conicalor tapered configuration that provides sufficient wall thickness t andcontrolled deformation of the nose portion when the recess isincorporated into the modified rear ferrule. Preferably, the outer wall50 has a generally uniform angle or taper as it extends between thereduced dimension of forward nose portion 52 received in the cammingmouth of the front ferrule and the enlarged diameter of rear flange 26″.Again, this provides controlled deformation of the rear ferrule so thatforward nose portion 52 is plastically deformed radially inward alongforward contact area 44 into gripping, sealed engagement with the outerwall of the tube. Note that in FIG. 4 the recess 40 is so shaped as toappear that the dimension t is constant, though it need not be. Forexample, if the recess 40 is formed such as in many of the illustrationsof FIGS. 14, 17 and 18, the tapered outer wall 50 provides a non-uniformthickness t between forward nose portion 52 and rear flange 26″.

The wall thickness “t” and the geometry and configuration of the rearferrule 22′ are selected for a particular application in order tobalance and properly align rear ferrule 22′ on the tubing and to assurethat the rear ferrule 22′ cooperates with the front ferrule 16′ toachieve the desired phase controlled sequential gripping operationduring pull-up to assure a proper seal on the tubing. During fittingpull-up, the rear ferrule 22′ applies a vector force against the outersurface of the tube end 13 that has both axial and radial components.The radial component force enables an axial friction force on the tubesurface to achieve excellent gripping and sealing action. This axialfriction force balances against an axial tube grip reaction force fromthe tube end 13.

The combined geometry of the tapered outer wall 50 along with the recess40 cause a “hinge” effect of forward nose portion 52. The selectedgeometry and configurations will depend on such factors including butnot necessarily limited to the materials used for the fittingcomponents, the tube material and wall thickness, the operating pressurefor the fitting, whether the rear ferrule is to be case hardened or not,and so forth. In order to maintain proper sequential gripping operationduring make-up, it is important that the rear ferrule 22′ forward noseportion 52 does not collapse too soon otherwise the front ferrule 16′may not have sufficient gripping force on the tube wall or an inadequateseal force between the front ferrule 16′ and the tapered camming mouth14′. If the rear ferrule 22′ collapses too late relative to the frontferrule, then the rear ferrule 22′ may not have adequate gripping forceon tube end 13.

The rear ferrule 22′ hinge effect directs the rear ferrule applied forceat the forward nose portion 52 against the tube wall at a significantradial vector angle from the tube surface. This ferrule applied forcevector B thus has a significant radial component while enabling thesignificant axial friction force. Thus, a smaller axial component forceapplied via the drive nut member 30′ sufficiently opposes the axial tubegripping reaction force in contrast to when the applied force issubstantially axial as in the prior art of FIGS. 1 and 1A. The rearferrule 22′ grip of tube end 13 thus approaches a toggle-like hingedaction. The smaller axial component force results in reduced drive nutmember 30 pull-up torque to achieve the same tube grip.

In addition, during fitting pull-up, this hinge characteristic directsthe tube reaction force through the rear ferrule 22′ generally towardthe central region of the rear ferrule driven surface 28′ that contactsthe drive surface of the nut shoulder 32′. This results in the reactionforces being more evenly distributed across the rear ferrule drivensurface 28′ to avoid or reduce high concentrations of stress, thusreducing or eliminating galling and reducing pull-up torque without lossof tube gripping force. In many cases it may be preferred that thereaction forces be directed in a direction generally normal to rearferrule driven surface 28′. The increased tube gripping force resultingfrom the applied radial force also imparts greater penetration orswaging of the rear ferrule 22′ nose portion 52′ onto tube end 13. Thisprovides an excellent tube grip and seal with lower applied torque, andalso provides greater resistance to vibration fatigue by providing aswaged region of high gripping pressure behind (i.e. axially rearward)of the tube stress riser created at the forward end of the nose of therear ferrule 22′. FIG. 28 illustrates this result, in that the stressriser region 400 where the nose penetrates tube end 13 is axiallyforward of a swaged region 402 of high frictional engagement between theferrule nose and the tube end. High frictional area or swage produces acollet effect that secures the ferrule on the tube wall and protects thestress riser region 400 from vibration. Good gripping action of the rearferrule forward flat contacting area 44 of the nose portion onto thetube is important for overall performance of the fitting, in contrast toany contact pressure between the rear ferrule rear flat contacting over42. In many cases, there is no need for a contact between rear contactsarea 42 and tube end 13.

Another benefit resulting from the reduced galling and lower pull-uptorque of the present invention is that re-make of the fitting isfacilitated. By “re-make” is simply meant that, in some applications,the user desires to separate a tube fitting after installation, possiblyto replace a valve, tubing or to perform other routine maintenance andrepair, and then to re-install the same fitting without replacing theferrules and/or nut or body. If the rear ferrule and drive nut havebecome galled, then the torque required for re-make of the fitting maybe prohibitive or impossible, or the fitting may not adequately re-seal.With the use of the present invention to significantly reduce oreliminate galling and reduce pull-up torque, re-make is facilitated.

Although the present invention is useful with many different materials,it has particular advantages when used with stainless steel fittings andtubing, including but not limited to 316 and 316L stainless tubing, butincludes in addition to other alloys, Hastalloy, Inconel, Monel alloys400 and 500, 254SMO and steel, and duplex stainless steel such as, forexample, SAF 2507. The present invention can be used with or withoutcase hardening on all or part of the surfaces of the ferrules asrequired.

With respect to case hardened ferrules or ferrules made of materialssubstantially harder than 316L stainless steel, the present inventionallows the fitting 10 to be properly pulled up with the desired phasecontrolled sequential gripping of the tube wall. If a conventionalferrule, particularly the rear ferrule, was case hardened or made of avery hard material, the ferrule would be too stiff to achieve properseal and grip of the tube wall. The present invention howeverfacilitates the use of ferrules of hard materials or that have been casehardened over part or all of their surface. Case hardening herein refersto the treatment of the ferrules in such a manner as to provide a carbonor nitrogen rich surface that substantially hardens the ferrule body ascompared to the underlying base metal, as is known to those skilled inthe art.

FIG. 5 illustrates another preferred embodiment of the rear ferrule inwhich the recess 40 has is defined by two different angles (an obtusetriangle). For example, the smaller first angle defined with the innersurface increases as it extends rearwardly from forward contact area 44toward the rear flange 26′. The larger second angle (approximately twicethe angular dimension of the first angle) increases as it extendsforwardly from rear contact surface 42 toward the nose region. Theseangles thus intersect at an axial position that is located beneath theintersection of the outer wall 50 with the rear flange. Accordingly, thestresses are more evenly distributed over the rear ferrule drivensurface 28′. Turning to FIGS. 6 and 7, the rear ferrule of the prior artarrangement of FIG. 1 is shown before and after make-up of the fitting.The fitting was subjected to a finite element analysis, the results ofwhich are particularly evident in FIG. 7. There, shaded regions in therear flange of the rear ferrule and the nut evidence the force andstress concentrations encountered upon make-up of the fitting.Particularly, a region of high stress concentration is designated atregion 60. Regions of progressively decreased stress concentration areidentified by numerals 62, 64, 66, 68, and 70. Thus, the large stressconcentration at the radial inner location of rear ferrule drivensurface 28′ results in increased torque during make-up and potentialgalling of the nut.

FIGS. 8 and 9 show another modified rear ferrule in accordance with theteachings of the present invention. This rear ferrule is the same asshown in FIG. 5. As particularly evident in FIG. 9, the region of highstress concentration is substantially reduced in size when compared toFIG. 7. This indicates that the stresses have been more uniformlydispersed over the rear face of the flange of the rear ferrule. Thus,the torque is reduced and the potential for galling is likewise reduced.

FIGS. 10 and 11 represent the rear ferrule shown and described in FIG.4. Here, the finite element analysis illustrates that the region of highstress concentration is substantially removed at the rear face and amore uniform distribution of stresses obtained. Again, the torque forcesassociated with make-up are thus reduced with the correspondingreduction in localized stress concentrations. The recess and conicalouter wall provide a radial component to the forces generated in thefitting and transferred through the rear ferrule while still providing adesired gripping and sealing of the tube.

The embodiment of FIGS. 12 and 13 also achieves these same objectives.The recess is of a slightly different configuration, i.e., the recess ismore sharply defined in the inner wall of the rear ferrule. It is alsoshifted slightly forwardly so that the deepest portion of the recess islocated forwardly of the rear flange. However, the outer wall is stillof conical configuration and in conjunction with the recess distributesthe stresses along the rear face of the rear ferrule.

As is apparent with the various embodiments described above, the recessand the tapered outer wall do not require a particular conformation toachieve the stress distribution and reduced torque for make-up of thefitting. In fact, a number of proposed alternative embodiments areillustrated in table form in FIG. 14. For example, the first row ofgeometries have a standard location that is generally defined as therear edge of the recess being located axially beneath the intersectionof the outer wall and the enlarged flange. The tear drop, righttriangle, rectangle, oval, square circular, obtuse triangle, curve, andcompound curve are various shapes that the recess may adopt. Moreover,the recess can be positioned at a forward location (second row), or arearward location where the deepest portion of the recess is positionedbeneath the enlarged flange (third row) while still adopting the variousconfigurations. Still further, the orientation of the shapes can bereversed as demonstrated by the various geometries in the fourth row orthe sixth row, or the recess may be defined by multiple recesses asshown in the geometries of the fifth and eighth rows. Alternatively, therecess or recesses may be enlarged as indicated in the seventh andeighth rows. Accordingly, the invention is not limited to the particularconfigurations shown and described in the earlier embodiments of FIGS.2–13, but may also be incorporated into selected other geometricalconfigurations.

With reference to FIGS. 15–20, another embodiment of the invention isillustrated. As noted herein above, the use of a recess 40 in the rearferrule 22′ significantly reduces stress concentrations at shoulder 32of the drive nut member 30′ by adding a radial component to the pull upforces. The provision of the tapered outer wall 50 further cancontribute to the radial component and stress distribution, as well ascontrolled deformation of the rear ferrule 22′ during pull up. Inaccordance with the embodiments of FIGS. 15–20, the rear ferrule isprovided with a contoured drive surface that further reduces stressconcentrations in the area of engagement between the drive nut member30′ and the rear ferrule 22′.

FIG. 21 illustrates in an exemplary manner typical pull up stressdistributions at shoulder 32 and the rear ferrule drive surface 28′,typical in cases that incorporate a recess 40 type structure in the rearferrule as described herein before. These stress concentrations arerepresented by the arrows 200. By comparing the stress distributions ofFIG. 21 and the stress concentrations in FIG. 7 (FIG. 7 beingillustrative of a rear ferrule that does not include a recess-type ornotch structure 40) it is apparent that the provision of the recess 40concept significantly and substantially reduces stress concentration onshoulder 32 as noted hereinbefore. This reduction in stressconcentrations is further evident from a comparison of FIG. 7 with FIGS.9, 11 and 13.

Although FIG. 21 is not an FEA representation, it illustrates the pointthat the use of the recess 40 may not in all cases entirely eliminatestress concentrations at the rear surface of the rear ferrule (albeitthe use of the recess or notch 40 greatly reduces stress concentrationsin comparison to a rear ferrule that does not include a notch orrecess). In the simplified representation of FIG. 21, stressconcentrations may exist for example at the radially inner and outerportions of the rear ferrule flange 26 (referred to herein as bi-modalstress concentrations as they can occur though not have to occur as tworegions of stress concentrations). These somewhat higher bi-modal stressconcentrations are represented by the heavier arrows in FIG. 21. Thepresent invention is thus directed to further reducing such stressconcentrations, with the results illustrated in FIG. 19, wherein thearrows represent a substantial elimination of pull up forceconcentrations using a modified rear ferrule drive surface and therecessed inner radius.

In accordance with this further aspect of the invention a two ferrulefitting is shown having a rear ferrule which is modified so as to reducefurther the pull up stress concentrations by substantially distributingthe stress concentration along the rear surface that engages nutshoulder 32 of the drive nut member 30′. As is shown in FIGS. 15–18,corresponding fitting components are shown in finger-tight positionpreparatory to final tightening.

With specific reference to FIGS. 15 and 16, the fitting comprises a body110 having a cylindrical opening 112 for receiving a tube end 113 thatbottoms on a counterbore 112 a. A tapered, frusto-conical cam mouth 114is located at the axial rear or receiving end of the opening 112. Afront ferrule 116 having a smooth, cylindrical, radially inner wall 118is closely received on tube end 113. The front ferrule 116 has a taperedouter surface 120 which engages tapered cam mouth 114 of the body 110.

Associated with the front ferrule 116 and located axially adjacent(i.e., in a rearward direction concentrically aligned with thelongitudinal axis of the fitting) is a rear ferrule 122 configured witha tapered nose portion 124 having a rearward tapered surface 127. Therear ferrule 122 also includes a radially extending rear flange 126having a contoured end face 128. The contoured face 128 includes arearward-facing driven surface 129 which is engaged by a respectivedriving surface 132 of the drive nut member 130.

The rearward tapered surface 127 of the rear ferrule 122 engages and mayhave, but not necessarily, substantially the same angle as a tapered camsurface 125 in the rear area of the front ferrule 116. The nose portion124 is joined with the rear flange 126 by a preferably tapered outerwall 131. In the illustrated embodiment the outer wall 131 tapers withan increasing radial dimension in the axially rearward direction. Theouter wall 131 could also be cylindrical, although it is preferred to betapered to further facilitate reduction of stress concentrations on thedriven surface 129.

The ferrules 116 and 122 are enclosed by a threaded drive nut member 130which includes a drive surface 132 that engages the driven surface 129of the rear ferrule 122. The drive nut member 130 threadably engages athreaded portion of the body 110. During tightening and make-up of thefitting, the drive surface 132 of the drive nut member 130 applies pullup forces against the driven surface 129 of the rear ferrule 122 todrive both ferrules axially forward (to the right as viewed in FIG. 16)into the fully engaged position shown in FIG. 19. The rear ferrule isconfigured so that upon forced engagement with the tapered cam surface125, the nose portion 124 deforms radially inward. This action isdesirable since it results in a tight gripping engagement of the rearferrule 122 inner cylindrical wall with the outer surface of the wall ofthe tubing 113.

In the embodiments illustrated in FIGS. 15–20, the contoured end face128 of the rear ferrule 122 may be rounded, curved, arcuate, or bowed orother curvilinear shape or combination of such shapes. Preferably butnot necessarily the contoured end face 128 has a portion of which is acontour in the form of a convex radius R. The center of the radius canbe, for example, internal to the ferrule body as shown in FIG. 18.However, those skilled in the art will readily appreciate that theorigin of the driven surface 129 can be located anywhere with respect tothe rear ferrule structure with the illustration of FIG. 18 beingprovided for illustrative purposes only. One aspect of the contoured endface 128 is that with the driven surface 129 in the form of a convexradius, a line contact 129 b (or reduced face to face radial contact) isformed initially with the nut drive surface 132, in a region between theinner and outer radial portions of the rear flange 126. The rear ferrulealso preferably includes a recess 140 which can be of any configurationas previously described herein above. Alternatively, the contoured endface 128 can be used with a rear ferrule configuration that omits therecess 140, as illustrated in FIG. 20.

Although the use of a radius or other curvilinear surface for thecontoured end surface 128 is desirable, there is a practical limit as tohow small that radius can be made. If the radius of curvature is madetoo small then there will possibly be undesired stress concentrationsdevelop in the center region of the contoured end face 128.

A distinct advantage of the contoured rear ferrule 122 is that pull upstresses between the nut drive surface 132 and the contoured end face128 of the rear ferrule 122 are more uniformly distributed across thecontoured end face 128 of the rear ferrule, thus reducing andsubstantially eliminating stress concentrations. This further reductionof stress concentrations on the drive nut member 130 reduces pull uptorque and reduces galling, thus facilitating re-make of the fitting.

It is important to note that although the illustrated embodiments showan initial contact between the rear ferrule 122 and the drive nut member130 as generally in the middle of the contoured end face 128, this isnot required in every application. The initial point of contact will bea function of the overall fitting design, including the geometry of thetapered outer wall 131, the recess 140, the rearward tapered surface127, the front ferrule 116 configuration and so forth. But in keepingwith a general aspect of the invention, the contoured end face 128 willbe convex or axially variant in the region between the radial inner andouter portions of the rear flange 126 so as to distribute more uniformlythe pull up forces acting on the drive nut surface 132 to reduce gallingand pull up torque as compared to a conventional rear ferrule designthat has a substantially flat non-contoured driven surface.

FIG. 20 illustrates an embodiment of the invention in which the rearferrule 122′ has a substantially cylindrical inner wall 150′, butotherwise includes the rear flange 126′ having a contoured drivensurface 128′ and a nose portion 124′ with a rearward tapered surface127′ and a tapered outer wall 131′.

FIG. 22 illustrates another embodiment of the invention wherein the rearferrule 22′ design can have the recess 40′ shifted axially rearward,generally within the axial dimension of the rear flange 26′.

With reference to FIGS. 23A–F, we illustrate a number of variations ofthe contoured end face 128. In FIG. 23A the contoured end face 128 isformed with an elliptical profile. In FIG. 23B, the contoured end face128 is formed by a blending of multiple radiuses such as sections 128 a,128 b and 128 c (dots on the drawing designate points of intersection ofthe arcs and not physical features of the end face). In FIG. 23C, theend face 128 includes a central portion 128 a having a first radiusprofile, and outer portion 128 b formed by a second radius profile. InFIG. 23D the end face 128 includes a central portion 128 a having aprofile formed by a radius and outer portions 128 b and 128 c formed asstraight surfaces (in section the surface appears straight, thoughrealized in the form of a conical surface). In FIG. 23E the contouredend face 128 includes an elliptical central portion 128 a and a straightouter portion 128 b. And in FIG. 23F the contoured end face 128 has aprofile formed by three geometric shapes, an elliptical central portion128 a, a straight outer portion 128 b and a radiused center portion 128c. In all the examples of FIGS. 23A–F the point made is that theselected profile and geometry for the contoured end face 128, as withthe earlier embodiments described hereinbefore, is designed to achievethe desired plastic deformation of the rear ferrule 122 hinge-like noseto achieve excellent gripping of the tube while also maintaining theproper sequential pull-up operation with the front ferrule.

With reference to FIGS. 24A–F, the present invention can also berealized by incorporating a contoured profile in the nut drive surface132. In these embodiments, the contoured end face 128 is conical.Alternatively, both the nut drive surface 132 and the contoured end face128 could be contoured. FIGS. 24A–F correspond to FIGS. 23A–F as to thecontour shape applied to the nut drive surface 132. Thus, FIG. 24Aillustrates an elliptical profile; FIG. 24B illustrates a multiplecircle profile; FIG. 24C illustrates a two radius surfaces; FIG. 24Dillustrates a radius surface and two straight portions; FIG. 24Eillustrates an ellipse contour with a straight portion; and FIG. 24Fillustrates a combination of a radius, straight and ellipse portions. Inyet another embodiment of FIG. 24G, the nut drive surface 132 can beformed of two straight portions that join at an apex 129D.

With reference to FIG. 25, in still a further embodiment, the rearferrule 522 include a recess 540 in the inner cylindrical wall. However,in this embodiment, the rear flat portion 542 is formed by a largerdiameter bore in the ferrule 522 body as compared to the diameter of thebore that forms the forward flat portion 544. By forming the rear flatportion 542 with a larger diameter, a single tool can be used to formthe recess 540 and the central bores through the ferrule 522 body. Thedifference in the two diameters is represented by the dimension D inFIG. 25. Note that recess 540 is positioned in the rearward portion ofthe ferrule 522 body. This provides an axially elongated flat portion544 that assists in maintaining the ferrule in alignment during assemblysince the rear flat portion 542 does not as closely surround the tube.Those skilled in the art will readily appreciate, however, that theenlarged diameter rear flat portion 542 can be used with many of therecess profiles illustrated herein and others, including multiple notchdesigns. The rear ferrule 522 may also include a contoured rear wall asin the embodiments described herein.

FIG. 26 illustrates another embodiment of the rear ferrule 22′. In thisembodiment, in addition to the double recesses 40′ in the centralthrough bore, the ferrule includes a recess 300 in the outer diametersurface 50′ of the ferrule. This recess 300 can be used as part of the‘hinge’ design to further control the plastic deformation of the ferrulenose portion 52′ during pull-up. FIG. 27 illustrates a further exampleof a rear ferrule 622 that incorporates the central recess 640, atapered outer diameter 650 having an outer diameter recess 300′, and thelarger diameter rear portion or radial flange 642 with a contoured orradius driven surface 628. The radial flange 642 is of a slightly largerdiameter than the forward surface 644, as in other examples herein, asrepresented by the dimension DD″ All of the actual dimensions andprofiles may be selected to cause the ferrule 622 to plastically deformwith desired loads against the tube surface and minimized loadconcentrations against the nut drive surface and also assure properdriving force into the front ferrule. As with the various other rearferrule designs illustrated herein, the various concepts of the rearferrule design can be used in a single ferrule fitting.

The ferrule illustrated in FIG. 27 includes the outer notch 300′. TheFEA illustration of FIG. 28 dramatically shows how this outer notch 300′produces a significant hinge effect at the nose portion 652 of the rearferrule. The outer notch 300′ is bounded by a radially extending crown302. This crown 302 functions to prevent the nose of the rear ferrule22′ from slipping (as, for example, in a telescoping manner) under thefront ferrule when the tubing is thin walled or otherwise easilydeformed during make-up of the fitting. Without the crown 302, as thethin tube wall collapsed the nose of the rear ferrule could be forcedout of the camming mouth of the front ferrule and slip under the frontferrule, preventing proper sequential pull-up and poor gripping byeither ferrule. Preferably, the crown 302 maintains contact with theinner camming mouth of the front ferrule during pull-up.

The invention has been described with reference to the preferredembodiment. Obviously, modifications and alterations will occur toothers upon a reading and understanding of this specification. It isintended to include all such modifications and alterations insofar asthey come within the scope of the appended claims or the equivalentsthereof.

1. A tube gripping ferrule for a metal tube fitting, the ferrulecomprising: a generally cylindrical interior wall through the center ofthe ferrule so that said ferrule can be installed over a metal tube end;said ferrule being case hardened over substantially its entire surface;an outer wall that axially tapers with a radially increasing dimensionfrom a front portion of the ferrule towards a back portion of theferrule; said front portion of the ferrule indenting and biting into anouter surface of a metal tube end after the fitting is assembled andpulled-up; said interior wall comprising first and second cylindricalportions, said first cylindrical portion being axially adjacent a frontedge of the ferrule and having the smallest interior wall diameter ofthe ferrule, said second cylindrical portion having a larger diameterthan said first cylindrical portion, wherein the tube fitting is a twoferrule tube fitting and comprises first and second components that arejoined together to install the tube fitting on a metal tube end andenclose two ferrules that are axially driven together when the tubefitting is pulled-up, wherein said ferrule having said first and secondcylindrical portions is a back ferrule in said two ferrule tube fitting.